The nickel-borocarbides ANi 2 B 2 C [A=Y, Ln (lanthanide), An(actinide)], crystallizing in the body-centred tetragonal LuNi 2 B 2 C-type structure, are classified according to the existence or coexistence of superconducting and antiferromagnetic states (AF). The magnetic features observed in polycrystalline (A,A')Ni 2 B 2 C solid solutions, adopting the same crystal structure, are reviewed and discussed. Published data on the magnetism in (A,Ln)Ni 2 B 2 C systems (ANi 2 B 2 C nonmagnetic, A=Y,La,Lu) indicate a gradual rise in the threshold content, x(m), in (Y 1 - x Ln x )Ni 2 B 2 C (Ln=Gd,Tb,Dy,Ho,Er) for the establishment of AF states. (A,A')Ni 2 B 2 C systems with magnetic end compounds show gradual variation in magnetic features when A and A' are both heavy Ln. The behaviour of (A,A')Ni 2 B 2 C systems of light A (Pr or U) and heavy A' (Dy or Tm) depends on the magnetic structures of the end compounds. In intermediate compositions, incomplete moment compensation in (Pr,Dy)Ni 2 B 2 C decreases T N , while different moment directions in the end compounds in (U,Dy)Ni 2 B 2 C lead to a directional frustration of ordered moments. Such a frustration in (U,Tm)Ni 2 B 2 C is related to different magnetic structures of the end compounds.